By Scott Williams
There are lots of popular exercise classes these days — Pilates, CrossFit, kickboxing, Peloton, yoga, and BodyPump, to name a few. Most of these incorporate movements where either the torso rotates or a limb moves across the midline of the body. What is the midline of your body and why have these movements been popularized? Broadly defined, it is a line that divides your body into right and left sides running from the tip of your nose through your navel and down between your feet, so that when your right hand moves towards your left hip you have crossed the midline of the body. Research suggests these movements that cross the midline are beneficial and important for a number of reasons.
Seventy years ago, researchers began to appreciate the importance of neurological developmental movement patterns from birth to 2 to 3 years of age. Many of these movement patterns were termed “cross crawl” because it was noted that as children learned to crawl they reached with their right arm and simultaneously lifted and brought their left hip forward toward their left elbow. This was the original cross crawl exercise that crossed the midline. This reciprocal and opposite limb movement, when the right arm extends and left leg flexes, was seen as a way for a growing infant to improve coordination and brain development. The right brain controls movement of the left side of the body and the left brain controls the movement of the right side, thus both sides of the brain are working simultaneously to produce a coordinated movement pattern.
These movements of crossing the midline were shown to be beneficial to strengthen infants’ core, develop balance, and improve coordination skills. And, as we continued to develop, we learned more complex movement patterns that involved balance, walking, running, twisting, and even more complex motor patterns used in athletics.
Neurodevelopmental therapists use exercises that cross the midline for young children with developmental delays as well as older individuals who have suffered strokes or other central nervous system disorders. Evidence has proven that patients incorporating similar exercise patterns improve gross motor coordination, balance, writing skills, eye-hand coordination, and simple walking.
Many people who live an active lifestyle have had some type of injury that causes them to alter key movement patterns. And even if you have been fortunate to have not had any injuries, simply getting older causes us to stop or modify certain movements. Think back to movements we did as children like running, jumping, swinging from the monkey bars, or playing kickball. In fact, most activities on a playground and most athletics involve movements of rotation where the trunk or an extremity cross the midline, like tennis, swimming, and any running sport. Now we have a plethora of opportunities to move across the midline as adults such as dancing, practicing yoga, or even playing kickball, but we often don’t do them enough to maintain mobility, balance, and eye-hand coordination, hence the popularity of the aforementioned classes.
To better explain anatomically, most of the muscles in your body do not travel in a straight vertical or linear line but are diagonal, and therefore produce some rotation about the axis they are generating movement on.
Many muscles in the above diagram produce forces that pull slightly horizontal or toward or away from the midline, causing rotational forces. In order to strengthen them, we need to pull our body or limb along that line of the muscle. For example, if you want bigger biceps you do a lot of arm curls, and if a muscle runs diagonally, it’s important to incorporate an exercise along the line of the muscle. This is another reason we need rotational movements or exercises that cross the midline. Unfortunately, we have become habituated to patterns of sitting and moving in a single plane or not crossing the midline on a routine basis.
Probably the most important reason to do more of these exercise movements is for joint and connective tissue health. Think about a hip joint, which is a simple ball and socket (see diagram previous page).
This design allows for movement in all three planes, often at the same time. If we become limited in our movement patterns we only move the ball in the socket in one or two planes. Rarely do we move through all three planes, and it’s even rarer that we take the joint through its full range of motion. This can have a negative effect on our joints and connective tissue, which rely on triplanar movement and mechanical load to produce fluid, which helps lubricate and maintain the health of the joint. Mechanical load is like gravity for your bone density. When we stop doing weight-bearing activities, bone density decreases. Similarly, it is important to engage mechanical joint load in all three planes, with full range of motion to maintain connective tissue, cartilage density, and lubricate the joint surfaces. This requires us to move our limbs across and outside of our body, not just in our usual patterns.
Hopefully understanding the importance of moving across your body gives you motivation to get out and do some movements that cross the midline and involve rotation of your trunk and limbs. The more varied, the better. There are plenty of yoga, cardio kickboxing, and music venues for dancing as well.
~ Scott Williams is a physical therapist and owns Synergy Healing Arts in Truckee. He has worked with the Chinese Olympic teams in Beijing, international soccer clubs, and cycling teams including T-Mobile and Garmin/Barracuda. He has lived in the area since 1996.
